The toxicology of carbon nanomaterials is the study of toxicity in carbon nanomaterials, such as fullerenes and carbon nanotubes.
Fullerenes A review of works on fullerene toxicity by Lalwani et al. found little evidence that C60 is toxic. The toxicity of these carbon nanoparticles varies with dose, duration, type (e.g., C60, C70, M@C60, M@C82), functional groups used to water-solubilize these nanoparticles (e.g., OH, COOH), and method of administration (e.g., intravenous, intraperitoneal). The authors recommended that the pharmacology of each fullerene- or metallofullerene-based complex be assessed as a different compound. Moussa et al. (1996–97) studied the in vivo toxicity of C60 after intra-peritoneal administration of large doses. No evidence of toxicity was found and the mice tolerated a dose of 5 g/kg of body weight. Mori et al. (2006) could not find toxicity in rodents for C60 and C70 mixtures after oral administration of a dose of 2 g/kg body weight and did not observe evidence of genotoxic or mutagenic potential in vitro. Other studies could not establish the toxicity of fullerenes: on the contrary, the work of Gharbi et al. (2005) suggested that aqueous C60 suspensions failing to produce acute or subacute toxicity in rodents could also protect their livers in a dose-dependent manner against free-radical damage. In a 2012 primary study of an olive oil / C60 suspension administered to rats by intra-peritoneal administration or oral gavage, a prolonged lifespan to almost double the normal lifespan of the rats was seen and significant toxicity was not observed. An investigator for this study, Professor Moussa, generalized from its findings in a video interview and stated that pure C60 is not toxic. When considering toxicological data, care must be taken to distinguish as necessary between what are normally referred to as fullerenes: (C60, C70, ...); fullerene derivatives: C60 or other fullerenes with covalently bonded chemical groups; fullerene complexes (e.g., water-solubilized with surfactants, such as C60-PVP; host–guest complexes, such as with cyclodextrin), where the fullerene is supermolecular bound to another molecule; C60 nanoparticles, which are extended solid-phase aggregates of C60 crystallites; and nanotubes, which are generally much larger (in terms of molecular weight and size) molecules, and are different in shape to the spheroidal fullerenes C60 and C70, as well as having different chemical and physical properties. The molecules above are all fullerenes (close-caged all-carbon molecules) but it is unreliable to extrapolate results from C60 to nanotubes or vice versa, as they range from insoluble materials in either hydrophilic or lipophilic media, to hydrophilic, lipophilic, or even amphiphilic molecules, and with other varying physical and chemical properties. A quantitative structural analysis relationship (QSAR) study can analyze on how close the molecules under consideration are in physical and chemical properties, which can help.
Carbon nanotubes
As of 2013, the United States National Institute for Occupational Safety and Health was not aware of any reports of adverse health effects in workers using or producing carbon nanotubes or carbon nanofibers. However a systematic review of 54 laboratory animal studies indicated that they could cause adverse pulmonary effects including inflammation, granulomas, and pulmonary fibrosis, which were of similar or greater potency when compared with other known fibrogenic materials such as silica, asbestos, and ultrafine carbon black. With reference to nanotubes, a 2008 study on carbon nanotubes introduced into the abdominal cavity of mice led the authors to suggest comparisons to "asbestos-like pathogenicity". This was not an inhalation study, though there have been several performed in the past, therefore it is premature to conclude that nanotubes should be considered to have a toxicological profile similar to asbestos. Conversely, and perhaps illustrative of how the various classes of molecules which fall under the general term fullerene cover a wide range of properties, Sayes et al. found that in vivo inhalation of C60(OH)24 and nano-C60 in rats gave no effect, whereas in comparison quartz particles produced an inflammatory response under the same conditions. As stated above, nanotubes are quite different in chemical and physical properties to C60, i.e., molecular weight, shape, size, physical properties (such as solubility) all are very different, so from a toxicological standpoint, different results for C60 and nanotubes are not suggestive of any discrepancy in the findings. A 2016 study reported on workers in a large-scale MWCNT manufacturing facility in Russia with relatively high occupational exposure levels, finding that exposure to MWCNTs caused significant increase in several inflammatory cytokines and other biomarkers for interstitial lung disease.
Toxicity The toxicity of carbon nanotubes has been an important question in nanotechnology. As of 2007, such research had just begun. The data is still fragmentary and subject to criticism. Preliminary results highlight the difficulties in evaluating the toxicity of this heterogeneous material. Parameters such as structure, size distribution, surface area, surface chemistry, surface charge, and agglomeration state as well as purity of the samples, have considerable impact on the reactivity of carbon nanotubes. However, available data clearly show that, under some conditions, nanotubes can cross membrane barriers, which suggests that, if raw materials reach the organs, they can induce harmful effects such as inflammatory and fibrotic reactions.
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